Thrust and flight path control decoupling system

ABSTRACT

Signals representative of the acceleration of an aircraft due to the change in flight path angle are coupled through a high pass filter (washout circuit) to obtain a short term compensation signal (Vcomp) which signal is further coupled to a low pass filter which provides short term integration to obtain the compensation signal ( Delta Vcomp) representative of change in speed in response to change in flight path angle. These compensation signals (Vcomp) and ( Delta Vcomp) are summed respectively with signals representative of longitudinal acceleration (or thrust control damping) and air speed error (or thrust control reference) to inhibit short term thrust control of the aircraft due to small flight path angle perturbations thereby improving the manual path control handling quality and the stability of the aircraft by the automatic control system. A modification of the system is disclosed for avoiding sensor noise developed by the Alpha (angle of attack) vane sensor by utilization of other inputs to the system signal processing.

United States Patent [191 Lam bregts l l THRUST AND FLIGHT PATH CONTROLDECOUPLING SYSTEM [75] Inventor: Antonius A. Lambregts, Renton.

Wash.

[73] Assignee: The Boeing Company, Seattle,

Wash.

[22] Filed: Dec. 20, 1973 [2i 1 Appl. No.: 426,852

Related U.S. Application Data {62] Division of Ser. No. 307,286, Nov I6,1972.

[52] US. Cl. i. 244/77 D; 235M502 [51] Int. Cl. B64C 13/18 [58] Field ofSearch 73/178 R, I78 T;

235/502, 150.21; 244/77 D; 340/27 R, 27 SS [56] References Cited UNITEDSTATES PATENTS 3,l28,967 4/l964 Hays U 244/77 D 3,522,729 4/1970 Miller244/77 D X 3,8l4,9l2 6/l964 Manke et al i. 244/77 D X PrimaryExaminer-Trygve M. Blix Assistant ExaminerStephen G. Kunin Allomey,Agent, or FirmConrad O. Gardner; Glenn Orlob P/ru/ Arr/runs 550301!AI/GZE or ATrAc'K ac SENSOR l I l l l I Aug. 26, 1975 5 7 ABSTRACTSignals representative of the acceleration of an aircraft due to thechange in flight path angle are coupled through a high pass filter(washout circuit) to obtain a short term compensation signal (V whichsignal is further coupled to a low pass filter which provides short termintegration to obtain the compensation signal (A V, representative ofchange in speed in response to change in flight path angle. Thesecompensation signals (V and (A V are summed respectively with signalsrepresentative of longitudinal acceleration (or thrust control damping)and air speed error (or thrust control reference) to inhibit short termthrust control of the aircraft due to small flight path angleperturbations thereby improving the manual path control handling qualityand the stability of the aircraft by the automatic control system. Amodification of the system is disclosed for avoiding sensor noisedeveloped by the an (angle of attack) vane sensor by utilization ofother inputs to the system signal processing.

JCCEL EKG- METER 5 :S/SUMMNG Ma i WWW/1E com/rec ELECT/wales 752(wimp/HEB I? 1 of 5 PATEHTED M525 975 ENSQQEQ USQE BE mm: $28 $55 Q3?uoh kwh Trams NQWEWW THRUST AND FLIGHT PATH CONTROL DECOUPLING SYSTEMThis is a division, of application Ser. No. 307,286 filed Nov. 16, 1972.

This invention relates to aircraft flight control and more particularlyto a means for improving thrust flight path control relationships.

Present flight control systems having automatic speed control utilizingthrust as a control parameter result in degradation in stability offlight path angle because thrust is a key parameter in determiningstatic flight path angle, and further, pitching moments associated withthrust changes cause dynamic pitch and flight path angle instability forconstant elevator position. To hold a constant flight path angle withautothrottle engaged requires therefore a constant coordination ofelevator inputs with thrust variations to compensate for thrust effectson the flight path angle.

When the flight path is controlled manually, degradation of the handlingquality of the airplane having these systems results. The above effectsin these known systems explains why it is actually more satisfactory forthe pilot to control both flight path and speed manually, rather thanflight path only with speed controlled by the autothrottle.

It is accordingly an object of the present invention to provide meansfor improving attitude and flight path stability, pitch control andspeed control coupling. and throttle response by minimizing undesiredthrottle activity in an aircraft having automatic speed control whereinthrust is utilized as a control parameter.

it is further an object of this invention to provide means utilizing theconversion principle of potential and kinetic energy of an elevatorcontrolled flight path for reducing throttle activity to obtaindecoupling of short term thrust control from flight path control therebyimproving the handling quality of manual flight path control and/orimproving stability of the combination autopilot and autothrottlesystems.

The above and other objects are achieved in accordance with a firstembodiment of the invention wherein path deviation information isutilized in the system signal processing to compute the relatedacceleration and speed deviation and provide first and secondcompensation signals for inhibiting autothrottle response to short termflight path deviations. More specifically signals representative ofpitch attitude (6) and angle of attack (a) are utilized in theaforementioned signal processing to provide the compensating signals.The first and second compensating signals are combined respectively withacceleration and speed representative signals of the prior art, viz., \7and V heretofore normally inputted to the autothrottle, to howeverprovide respectively compensated acceleration and speed representativesignals V and V for inhibiting autothrottle responseJn accordance withthe teachings of the present invention.

In accordance with a second embodiment of this in vention theaforementioned signal processing to develop the first and secondcompensating signals utilizes signals representative of pitch attitude(6) and angle of attack (0:) although the mathematical counterpartsthereof are actually utilized and developed respectively from V, and AThrust and V and wherein the equivalent gains required are obtained fromthe speed equation. This second embodiment eliminates the use of the avane sensor and noise resulting therefrom in this system and stillprovides pitch attitude 0 and angle of attack a representative signalsfor system signal processing.

Further features and advantages of the invention will readily becomeapparent from the following specification and from the drawings, inwhich:

FIG. 1 is a block diagram of a system for providing energy compensatedautomatic thrust control utilizing signals representative of 6 and a inaccordance with a first embodiment of the present invention;

FIG. 2 is a schematic circuit diagram of the system shown in block formin FIG. 1;

FIG. 3 is a block diagram of a system for providing energy compensatedautomatic thrust control however utilizing signals representative of V.AT and V in accordance with a second embodiment of the presentinvention;

FIG. 4 is a block diagram of a means alternate to that shown in FIG. 3for developing compensation signals limited to a predetermined smallvalue in response to high rates of change of flight path in order toallow immediate control of large air speed errors;

FIG. 5 is a schematic diagram of the system shown in block form in FIG.3 incorporating however the feature of filter time constant programmingshown in FIG. 4;

FIG. 6 is a schematic diagram of a further energy compensation systemembodiment similar to the system shown in FIG. 5 however utilizing anEPR (engine pressure ratio) or N, (fan speed) signal source forproviding an input signal representative of thrust;

FlG. 7 is a series of graphs illustrative of the values of the variabletime constants programmed as functions of air speed error andlongitudinal acceleration for the high and low pass filters utilized inthe systems of FIGS. 5 and 6.

Turning now to a brief analysis of the problem presented in thrust andflight path control deemed helpful to a more complete understanding andappreciation of the present system, it will be noted as hereinbeforebriefly mentioned that during manual speed control, the pilot generatesfar less throttle activity than that generated in present state of theart systems, while holding a speed within the same tolerances. Thereasons for minimum throttle activity by the pilot compared to state ofthe art systems are first, the pilot does not attempt fine control thelast knot or so of speed error by changing thrust; second, the pilotutilizes elevator instead of thrust to control small speed errorsassociated with flight path errors; and third, since thrust does notchange automatically in response to small speed errors, the flight pathis stable, making control of flight path stable and causing less inducedair speed errors.

A further understanding of the pilot's speed flight path controltechnique may be had by considering the following approximate staticaircraft force equations:

From (1) follows 3 sin y T-D/W where T total thrust D total drag Wweight 'y flight path angle Since the airplane is being operated veryclose to or at minimum drag speed (V), where essentially, the steadystate flight path angle is only a function to thrust and is independentof speed. With thrust constant, the speed is controlled by the elevatorwhich has no authority to change 7 statically, and is instrumental onlyin shifting the equilibrium between thrust, lift and drag, visualized bythe parameters pitch attitude 6. angle of attack a and speed V. In thedynamic process of shifting this equilibrium, the total energy of thesystem is conserved, neglecting the relatively small perturbation due todynamic variation in drag.

4 mg (In, dh) /2 m (V,,+ dv) constant or 5 dh/dv =V /g where m mass ggravity constant h initial altitude V initial speed dh altitudeperturbation (IV speed perturbation For an approach speed of 240 ft/sthen and for a knot maneuver margin, the airplane may be displaced 63 ftvertically. This is generally adequate to control small perturbationswithout changes in thrust setting, once the airplane is thrust-trimmedfor the desired flight path.

The above discussed principles of the balance of total energy areutilized in the system embodiments of the present invention forimproving stability of flight path control, reducing flight path/speedcontrol coupling and minimizing throttle activity by what may be termedenergy compensated speed control." In energy compcnsated speed controlhereinafter described in detail, when the command is to fly a constantpath, the speed perturbations induced by path deviations areautomatically nulled by eliminating the path error. Further, where theautothrottle is temporarily inhibited from reacting to such speederrors, the commanded path correction can be made without theinterference of changing thrust resulting in substantially more stableattitude and path control while significantly reducing throttleactivity.

The aforementioned speed perturbations due to path deviations can becomputed from 9 and a through the following formula:

7 dV g/V,,,V,, sin A (1 dt or 8 dV/dt g A (B-a) v compensation, and

g. A v gfA (9-0:) dt AV compensation.

The formula (6) is an approximation and is accurate particularly in thelow frequency range of the phugoid. In the frequency I) drag Coefiicicntchange per it i a where q dynamic pressure s wing area w weight ggravity acceleration constant This term (ll) may be included in theformulas (8) and (9) of the compensation signals.

is fed through a washout circuit. Av is obtained by feeding V through afilter circuit having a long time lag characteristic which therebyprovides integration over relatively short term periods termed pseudointegrator type signal processing. A pseudo integrator type circuitinstead ofa pure integrator circuit is required to prevent continuousstorage of the compensation signal AV,.,,,,,,, which would cause an airspeed bias. The resulting energy compensated speed control system forproviding the aforementioned type signal processing is shown in blockdiagram form in FIG. 1 where:

d(' a drag cuefficient change per unit change in 01 1 l q 7 pV dynamicpressure V air speed s wing area S LaPlace operator 1| washout timeconstant 1" pseudo integrator time constant \V weight v v lDIlIII Thecompensated signals V and V provided by the present system signalprocessing are coupled to the autothrottle inputs instead of therespective uncompensated signals V and V utilized in previous systemswithout any requirement of modification of autothrottle control lawelectronics downstream of the previous autothrottle inputs.

Turning now to FIG. 2 it will be seen how in an exemplary schematic formshowing the types of circuits required, the signal processing developedin the preceding and shown in block form in FIG. 1 may be provided. Morespecifically the system of FIG. 2 is illustrative of a means fordeveloping compensated signals representative of longitudinalacceleration V (thrust control damping) and air speed error V (thrustcontrol reference) from signals representative of sensed longitudinalacceleration (thrust control damping) V, air speed error (thrust controlreference) V pitch attitude (2, and angle of attack 01. Thesecompensated signals V and V are coupled respectively to the autothrottleinputs instead of the signals V and V heretofore coupled thereto. Pitchattitude sensing means 210 provides signal representative of pitchattitude (6) and angle of attack sensing means 220 provides a signalrepresentative of angle of attack (aa), these signals being combined bycoupling to summing amplifier circuit means 224. This amplifier circuit224 provides at the output thereof a signal representative of which iscoupled to the input washout (high pass filter) circuit means 226. Theoutput of washout circuit means 226 comprising the compensation signal Vand a third signal V representative of longitudinal accelerationprovided by the attitude compensated longitudinal accelerometer in theautothrottle means 238, are coupled to summing amplifier circuit means240 to provide a signal (V) representative of compensated longitudinalacceleration (thrust control damping) for coupling to autothrottle 238and utilization by the autothrottle computer electronic circuits of theprior art.

The output of the washout circuit means 226 (comprising theaforementioned compensation signal V is coupled to the input of pseudointegrator (low pass filter) circuit means 204 to obtain an outputcompensation signal (A V which is the air speed error correction termfor flight path error. The output from circuit means 234 comprising theA V,.,,,,,,, signal, and a sig nal representative of air speed error (Vobtained from air speed error sensing means 228 after demodulation incircuit 230, are coupled to summing amplifier circuit means 232 toobtain a signal (V representative of compensated air speed error (thrustcontrol reference) for coupling to autothrottle 238 and utilization bythe autothrottle computer electronic circuits of the prior art.

The embodiments hcreinbefore discussed for developing the compensatedsignals for coupling to the autopilot system rely on the use of an a-vane sensor. However, noise developed from this input sensor andreplacing the pitch attitude 6 and angle of attack a representativesignals as inputs to the system by their mathematically derivedcounterparts, viz., as derived from signals representative of V, AThrust and V in the following manner for use in further embodiments ofthe invention hereinafter described.

Recalling that equation (11) utilizing angle of attack ((1) informationdefined the compensation signal:

and that the forward acceleration of an aircraft is defined by:

Combining (II and (b) yields Instead of using signals representative of0 and a for providing the compensation signal V it is possible as seenfrom the preceding expression to use the parameters: V measured by anattitude compensated accelerometer. AT derived from the throttledisplacement or other thrust representative signal, and AV measured bythe air speed indicator, in signal processing by circuits arranged inthe manner now shown in block form in FIG. 3 to provide the compensationsignal comP- ln the turbulent air, a fluctuates rapidly andimplementation of equation utilizing a to provide the compensationsignals V and AV results in considerable throttle activity. It should befurther noted that it is ditficult to filter out the turbulence noise onthe a signal developed from an a -vane sensor while retaining meaningfulor -information.

In equation (c), which is mathematically identical to equation l l J,the term D AV is normally very small since the airplane is operated nearthe minimum drag point where D 0. However, this term reflects almosttotally the fluctuation in the compensation signal V due to turbulence.

By omitting this term we get the desired compensation signal containingall the meaningful information to achieve the criginal goal of thrustand flight path decoupling without introducing throttle activity due toturbulencenoise signal components.

The required signal representative of AT may be derived from thethrottle rate in the following manner:

e T f 3 (it where 8 throttle displacement Since only short terminformation is needed the integration can be accomplished by a pseudointegrator (low pass filter) circuit 312 coupled in series circuit pathwith throttle servotachometer means 308 and circuit 310 representativeof engine transfer function (Engine T.F.) to provide a signalrepresentative of s W Al where my ransfer function of low pass filtercircuit 3 l 2 The change in thrust is related to the change in throttlcposition by the engine transfer function G (8), in the following manner:

Combining the equations (f) and (g) yields Circuit 310 representative ofthe engine transfer function IG(S) is a known transfer function whichcan be implemented more specifically by circuitry as shown in moredetail in the schematic of FIG. 5. A signal representative of 8 iscoupled to circuit 310 from the throttle servo-tachometer 308 shown inFIG. 3 which is normally part of autothrottle computer electronics 238as shown in FIG. 5.

Substituting equation (h) into equation (d) yields the compensationsignal and the compensation signal representative of AV is obtained bycoupling the compensation signal representative of V through pseudointegrator (low pass filter having a time constant 1' circuit 234 sothat TIS The compensation signal representative of V is combined withthe signal representative of V by coupling the output of washout circuit226 to adder means 240 (comprising a summing amplifier circuit of thetype shown in more detail in FIG. 2) to provide the compensated signal Vrepresentative of compensated longitudinal acceleration (thrust controldamping) for coupling to autothrottle. In similar manner thecompensation signal representative of AV is combined with the signalrepresentative of V in summing amplifier 232 to provide the compensatedsignal V representative of compensated air speed error (thrust controlreference) for utilization by autothrottle.

Turning now briefly to a comparison of system block diagrams shown inFIGS. 3 and 4, it will be noted that the processing of the signalsrepresentative of and in the system of FIG. 4 are different from theprocessing of these signals in the system of FIG. 3 only in that meansare provided for varying the values of time constant 1'. in the highpass filter circuit (washout) means 411 and the time constant 1 in thelow pass filter circuit (pseudo integrator) means 413 in the circuit ofFIG. 4 compared to the predetermined fixed values thereof incorresponding filter circuit means 226 and 234 in the circuit of FIG. 3.These time constants r and 1- in filter circuit means 411 and M3respectively of the system of FIG. 4 are made to vary as a function ofthe sum of air speed error V and, forward acceleration (V) in such amanner that increasing air speed errors and forward accelerationdecrease these filter circuit time constants thereby effectivelylimiting the energy compensation function in the system of FIG. 4 to airspeed errors smaller than about 45 knots. Representation of differentvalues of time constants T and 1' as programmed for various values of Vand is shown in the graphs of FIG. 7 and the system features andadvantages resulting from time constant programming in the respectivefilter circuits will be described hereinafter in detail in connectionwith the description of these filter circuits as implemented in thesystems of FIGS. 5 and 6. The equivalent circuit schematic for thesystem block diagram of FIG. 4 is given in FIG. 5 which however showsfurther specific circuitry for the development of the signalrepresentative of An important reason for utilizing the feature ofvariable time constant filtering means 411 and 413 as shown in thesystem of FIGS. 4 and 5 rather than high and low pass filters 226 and234 having predetermined time constants as in the system of FIG. 3 isthat for certain types of commanded flight path changes such as in glidescope captures and go-around maneuvers or drag changes due toconfiguration changes, large air speed errors would occur for high ratesof change in flight path in a system such as FIG. 3 without immediatecorrection of thrust and, hence it may be desirable to utilize the FlGS.4 and embodiments where it is desired to limit energy compensation ofspeed control to air speed errors occurring below a predetermined smallvalue.

Turning now to the block diagram of FIG. 4 it will be seen briefly howthe compensation signals (V and AV are generated for use in an energycompensation of speed control system having a mode of operationresponsive to small air speed errors only. In FIG. 4 it will generallybe noted that circuit means 421 and 422 are provided for multiplying theloop gain in the respective filter circuits 411 and 413 by signalsrepresentative of the absolute sum of the amplified air speed error andforward acceleration, to which signals a positive bias signal is addedto provide programming control signal Y and which bias insures minimumloop gains (11,) and (1/7 respectively in the variable high pass filter411 (washout) circuit and the variable low pass filter 314 (pseudointegrator) circuit respectively when both V and V are zero. The gainsKy and K; in time constant programming means 414 are selected toincrease the respective loop gains of washout circuit 411 and pseudointegrator circuit 413 for larger values of speed error or acceleration(e.g., a factor 0.4 per knot air speed error and a factor 5 perknot/second acceleration respectively) so that in an energy compensatedspeed control system, e.g., as shown in detail in the circuit schematicof FIG. 5, the compensation signals (Y and Av are quickly reduced in theevent of substantial air speed errors and/or acceleration and contributelittle to the compensated output signals and coupled to the autothrottleso that the autothrottle reverts temporarily to the original speedcontrol until air speed error and acceleration are reduced to low valuesand the flight path has stabilized.

The complete schematic diagram shown in FIG. 5 utilizes time constantprogramming as shown in block form in FIG. 4 for the high pass (411) andlow pass (413) filter circuit means which develop the respectivecompensation signals (V and AV Also it should be noted that in thesystem of FIG. 5, the signal representative of 5 .1 is shown developedfrom signals representative of 8 generated by throttle servo-tachometermeans within the autothrottle computer electronics in the mannerhereinbofre discussed only briefly in connection with the block diagramdescription of FIG. 3.

More specifically, in apcordance with the embodimerit of FIG. 5 a signal(5 representative of the rate of change in throttle position is coupledfrom autothrottle computer electronics 238 and more specifically fromthrottle servo-tachometer means 239 to the input of circuit means 310representative of engine transfer function to develop a signal (-AT)representative of the rate of change of thrust. Since only short terminformation is desired, the signal (AT) representative of the rate ofchange of thrust is coupled through low pass filter (pseudo integrator)circuit 312 to provide a signal 8 w 'AT) representative of short termacceleration of the aircraft due to thrust, to a first input of summingamplifier circuit 503. A signal (+V) representative of longitudinalacceleration is coupled to a further input of summing amplifier circuit503 to provide an output signal representative of the acceleration ofthe aircraft due to deviation from the flight path. This output signaltaken at the output of summing amplifier circuit 503 is coupled tovariable high pass filter (washout) circuit 411 for providing at theoutput thereof a compensation signal (V,,,,,,,,) which is summed insumming amplifier 240 with a signal representative of longitudinalacceleration to provide a signal (V) representative of compensatedlongitudinal acceleration for coupling to autothrottle means 238 for useas a hew thrust control damping signal replacing V. A multiplier circuit421 is connected to provide feedback gain multiplication of amplifier A4in response to the amplitude of control signal Y provided by timeconstant programmer circuit means 414. Input signal X of multiplier 421being the output of amplifier A4 is multiplied in magnitude by a factorproportional to the magnitude of the second input signal Y to multiplier421, whereby Y is the output of the washout and pseudo integrator timeconstant programmer circuit 414. The time constant 1', of high passfilter circuit 411 is thereby controlled by and is inverselyproportional to the amplitude of control signal Y. The compensationsignal (V developed at the output of variable high pass filter circuitmeans 411 is utilized to provide a further compensation signal (Av atthe output of low pass filter circuit means 413 which is representativeof air speed error due to deviation from the flight path of theaircraft. This further compensation signal Av is summed in summingamplifier 232 with a signal representative of air speed error to providea signal V representative of compensated air speed error for coupling toautothrottle means 238 for use as a new thrust control reference signal.The time constant of variable low pass filter cir cuit means 413 isresponsive to the amplitude of control signal Y, being the second inputof multiplier circuit 427 which is coupled in the feedback loop ofamplifier A7 for multiplying the feedback X of amplifier A7, which isthe first input to multiplier circuit 427, by a factor proportional toY. The time constant 1', of low pass filter (pseudo integrator) circuitmeans 413 is therefore inversely proportional to the amplitude ofcontrol signal Y. A first signal representative of longitu dinalacceleration (V) and a second signal representative of air speed error(V,;) are amplified and combined in time constant programmer circuitmeans 414 and a bias signal (+bias) is added to provide a time constantprogramming control signal Y at the output of time constant programmercircuit means 414 which establishes predetennined minimum loop gains invariable high pass filter circuit means 411 and variable low pass filtercircuit means 413 respectively when signals representative of V and \7are both equal to zero. The amplifier circuit A9 and further amplifiercircuit A10 cou pled in series circuit between the input signalsrepresentative of and V and the output terminal 498, providesamplification K and Kffor respectively increasing the loop gain ofwashout circuit 411 and pseudo integrator circuit 413 so that thecompensation signals (V and AV are amplitude limited so as to compensate only for air speed errors smaller than about 5 knots which areinduced by flight path deviations.

It was previously noted in connection with the description of the systemof FIG. 5 and also in FIG. 6 that variable time constant 71 and 1'programming was utilized in the high and low pass filter circuits 41 1and 413 respectively under the control of programming control signal Y.Exemplary plots of these time constants are shown in FIG. 7. Now from ananalysis of autothrottle and airplane dynamics it has been noted that aknown type autothrottle controls air speed errors efficiently forfrequencies below 0.1 rad/sec in an exemplary jumbo jet type airplane(Boeing type 747) utilizing such autothrottle. The cutoff frequency forthrottle operation is therefore preselected at (H rad/sec, resulting ina nominal time constant 7 in the present energy compensation system of10 seconds. Above 0.] rad/sec the short term compensation signal therebycancels the elevator induced signal representative of acceleration Toobtain reasonably accurate integration above O.l rad/sec with the pseudointegrator circuit 413, the time constant T2 must be at least severaltimes greater than 1-,. Hence, 1' equal to about 50 seconds was chosen.The preselected value of r, is also influenced by the amount ofstability improvement nee essary and the maximum air speed errorspermitted during maneuvering with the present energy compensation systemin an active condition (controlling the autothrottle 238) and variestherefore for different airplanes depending upon airplanecharacteristics. Generally, the stability of the present system improveswith increasing time constant 1' (while also the air speed errors duringmaneuvers increase). The values of the variable time constants T1 and rprogrammed by the signals V and V is given in FIG. 7 for theabovementioned type aircraft (Boeing type 747). The rapid decrease in'r, and 1' for increasing V and can be observed, which results in thelimitation of the air speed errors which are allowed not to becontrolled immediately by the present system.

Now it should be noted that the engine transfer function as representedby circuit 310 of FIG. 5, is unique for a given airplane under a singleset of flight conditions. Generally, this transfer function does notchange appreciably in the limited range of operating conditions of theautothrottle. The equivalent circuit representative of the enginetransfer function can therefore be comprised of fixed circuit componentsas shown in cir cuit 310.

Generally, the response of engine thrust to throttle inputs is describedby a first order lag. The type JT9F engine manufactured by Pratt andWhitney and utilized on the Boeing type 747 airplane for exampleresponds in the higher thrust regions with a first order lag timeconstant of approximately 1.5 seconds. In the engine transfer functionmodel circuit 310 this would require R C to be 15, while the ratio of R/R in the circuit 310 is dictated by the static thrust gain per unitchange of throttle position.

Deviation of the engine as represented by the circuit 310 from actualengine performance under a preselected set of conditions affects theperformance of the energy compensation system of FIG. 5. The maindeviation occurs with thrust change per degree of throttle positionchange from preselected conditions, and within the range of variation ofthis parameter normally encountered by the system the energycompensation system of FIG. 5 will operate satisfactorily although notoptimally everywhere. An alternate approach to utilizing transferfunctio n circuit 310 for deriving a signal representative of AT for thepresent energy compensation system is to use another parameter that moreclosely represents thrust throughout the operating range, such as EnginePressure Ratio (EPR) or fan speed (N in the manner shown in FIG. 6.Although the energy compensation system embodiment of FIG. 6 requiresone additional sensor input, the signal source representative of EPR orN does not require throttle rate pseudo integration or the enginetransfer function signal processing circuits as shown in the system ofFIG. 5. Since the total thrust may vary due to the failure of one enginethe system may take this into consideration by providing a summing ofall four ingine EPRs each with of the thrust gain constant.

It should be noted from FIG. 5 that the compensation signal AV providedat the output of low pass filter circuit means 413 is summed with thesignal (V representative of air speed error in summing amplifier circuit232 to provide the compensated air speed error signal (\7,,-) which iscoupled to the autothrottle computer circuit means 238 for utilizationas the improved thrust control reference signal, replacing the signal Vutilized by prior art autothrottle computer circuit means.

Proceeding now to a further description of signal pro= cessing in thesystem of FIG. 5 and more particularly as utilized to generate the timeconstant programming control signal Y, and the manner in which controlsignal Y controls the time constants 1', and 1 of washout and pseudointegrator circuits 411 and 413 respectively to further control theamplitude of compensation sig nals \v and AV,.,,,,,,,, it will be notedthat the time constant programming control signal Y is generated at theoutput terminal 498 of washout and pseudo integrator time constantprogrammer circuit means 414. In circuit means 414, the signalrepresentative of air speed error (V,;) and acceleration are summed withmultiplication gains K and KF, respectively, in summing amplifiercircuit means A9. The output of summing amplifier circuit means A9,provides a signal representative of the expression K V K}. V which iscoupled through amplitude detector circuit means comprising a pair ofdiodes and added with a positive bias signal in amplifier circuit meansA10 to provide time constant programming control signal Y at outputterminal 998 which is equal to lK V K,- constant. THe detection of theamplitude or absolute value of the signals in accordance with thefollowing expression Ky V K V is utilized to insure negative feedbackgains for the variable low pass and high pass filter circuits 413 and411 respectively. The bias is chosen to yield minimum loop gains 1/1,and 1/1 for the respective filter circuits when K, V,; K V 0. For thecondition where the signals represented by the expression [Ky V K,- Vl 0the system of FIG. 5 is equivalent to the system of FIG. 3. When thesignals representative of the expression Ky V,; K i V increasesubstantially, such as during glide slope capture maneuvers indicativeof a buildup of substantial air speed errors, the amplitude of the timeconstant programming control signal Y increases so as to providedecreasing washout and pseudo integrator time constant thereby causingreduction in the rate of increase in amplitude of compensation signals Vand AV For larger amplitude signals representative of the expression KV,; Ky. V the respective time constants decrease so that the amplitudesof compensation signals V and AV are rapidly reduced to zero valuesthereby causing the autothrottle to revert to conventional speed controluntil air speed error and acceleration are reduced below predeterminedvalues, e.g., air speed errors are reduced below a predetermined valueof knots. In simulation testing, it was found that with the system ofFIG. 5, the air speed errors could be held within i 5 knots for normalglide slope capture or go-around maneuvers.

What is claimed is: l. in combination an autothrottle control system foran aircraft having a first input coupled to first means for providing asignal representative of longitudinal acceleration information of saidaircraft, and a second input coupled to second means for providing asignal representative of air speed error of said aircraft;

signal processing means responsive to signals repre sentative of pitchattitude and angle of attack information of said aircraft for providinga first compensation signal representative of longitudinal accelerationof said aircraft induced by short term flight path angle changes and asecond compensation signal representative of the deviation of air speeddue to short term flight path angle changes; third means for combiningsaid first compensation signal with said signal representative oflongitudina] acceleration information of said aircraft; and

fourth means for combining said second compensation signal with saidsignal representative of air speed error of said aircraft.

2. The invention according to claim 1 wherein said third and fourthmeans comprise summing amplifiers.

3. In combination;

an aircraft autothrottle having first and second input terminals forreceiving signals representative of longitudinal acceleration and airspeed error; pitch attitude sensing means for providing a first signalrepresentative of pitch attitude of the aircraft; angle of attacksensing means for providing a second signal representative of angle ofattack of the air craft; first summing amplifier means for combiningsaid first and second signals and providing a third signal; firstwashout circuit means responsive to said third signal for providing afirst compensation signal; attitude compensated longitudinalaccelerometer means for providing a fourth signal representative oflongitudinal acceleration; second summing amplifier means responsive tosaid fourth signal and said first compensation signal for providing asignal representative of compensated longitudinal acceleration;

first coupling means for coupling said signal representative ofcompensated longitudinal acceleration to said first input terminal;

for inhibiting autothrottle response to speed perturbations induced byflight path deviations comprising:

first means for generating a first compensation signal in accordancewith the expression second means for generating a second compensationsignal in accordance with the expression wherein the above expressions gis gravity acceleration, A 6 is change in pitch attitude, A a is changein angle of attack, C is drag coefficient change per unit change in a qis dynamic pressure, s is wing area, and w is weight;

third means for combining said first compensation signal with the signalinput to an autothrottle representative of longitudinal acceleration;and

fourth means for combining said second compensation signal with thesignal input to said autothrottle representative of air speed error.

5. In an aircraft authrottle control system having a first autothrottleinput signal representative of longitudinal acceleration and a secondinput signal representative of air speed error:

first means for generating a third signal representative of change inflight path angle;

second means for generating a fourth signal representative of change indrag with respect to change in angle of attack multiplied by the productof dynamic pressure times wing area divided by the weight of theaircraft;

third means for summing said third and fourth signals thereby providinga fifth signal;

a washout circuit;

fourth means for multiplying said fifth signal by the gravityacceleration constant and coupling the product to said washout circuitto provide a first compensation signal;

fifth means responsive to said first compensation signal for providingpseudo integration of said first compensation signal to provide a secondcompensation signal;

sixth means for summing said first compensation signal with said firstautothrottle input signal to provide a compensated first autothrottleinput signal; and

seventh means for summing said second compensation signal with saidsecond autothrottle input signal to provide a compensated secondautothrottle input signal.

6. In an autothrottle for an aircraft having first and secondautothrottle input signals representative of longitudinal accelerationand air speed error, means for compensating said first and secondautothrottle input signals comprising:

first summing circuit means having a plurality of input terminals and anoutput terminal;

throttle servo-tachometer means, circuit means representative of enginetransfer function of the aircraft, and pseudo integrator circuit meansconnected in series circuit with a first of said plurality of inputterminals;

second circuit means for coupling said first signal representative oflongitudinal acceleration to a second of said plurality of inputterminals;

washout circuit means coupled to said output terminal for providing afirst compensating signal; third circuit means for combining said firstautothrottle input signal representative of longitudinal accelerationwith said first compensating signal to provide a compensated firstautothrottle input signal;

further pseudo integrator circuit means responsive to said firstcompensating signal for providing a second compensating signal; and

fourth circuit means for combining said second input signalrepresentative of air speed error with said second compensating signalto provide a compensated second autothrottle input signal. 7. Theinvention ofclaim 6 wherein the time constant of said washout circuitmeans and the further time constant of said further pseudo integratorcircuit means vary as a function of the sum of air speed and forwardacceleration of said aircraft.

8. The invention of claim 6 wherein said washout cir cuit means and saidfurther pseudo integrator circuit means comprise respectively first andsecond variable time constant filtering means.

9. The invention according to claim 8 further including time constantprogramming means responsive to increasing air speed errors and forwardaccelerations of said aircraft for decreasing the respective timeconstants of said first and second variable time constant filteringmeans.

10. The invention according to claim 8 further including time constantprogramming means for multiplying the respective loop gains of saidfirst and second variable time constant filtering means.

11. The invention according to claim 10 wherein said time constantprogramming means comprises:

first amplifier means responsive to air speed error for providing anamplified air speed error signal;

second amplifier means responsive to forward acceleration for providingan amplified forward acceleration signal;

a positive bias signal source; and

means for providing the absolute sum of said amplified error signal andsaid forward acceleration signal and adding to said sum said positivebias signal to provide a programming control signal for multi plyingsaid respective loop gains of said first and second variable timeconstant filtering means.

12. The invention according to claim 11 wherein the gain factor of saidfirst amplifier means is 0.4 per knot air speed error and the gainfactor of said second ampli' fier means is 5 per knot per secondacceleration. 13. In an aircraft autothrottle control system: firstcircuit means for providing a first signal representative of rate ofchange in throttle position;

second circuit means representative of engine transfer function of saidaircraft responsive to said first signal for providing a second signalrepresentative of rate of change of thrust;

pseudo integrator circuit means responsive to said second signal forproviding a third signal representative ofshort term acceleration ofsaid aircraft due to thrust;

third circuit means for providing a fourth signal representative oflongitudinal acceleration of said aircraft;

fourth circuit means comprising a summing amplifier circuit responsiveto said third and fourth signals for providing a fifth signalrepresentative of acceleration of said aircraft due to deviation fromthe flight path;

fifth circuit means comprising a washout circuit responsive to saidfifth signal for providing a compensation signal;

sixth circuit means comprising a summing amplifier responsive to saidfifth signal and said compensation signal for providing a signalrepresentative of compensated longitudinal acceleration for coupling toautothrottle for utilization as a thrust control damping signal;

seventh circuit means comprising a pseudo integrator circuit responsiveto said compensation signal for providing a further compensation signalrepresentative of air speed error due to deviation from flight path;

eighth circuit means for providing a sixth signal representative of airspeed error; and

ninth circuit means comprising a summing amplifier responsive to saidsixth signal and said further compensation signal for providing a signalrepresentative of compensated air speed error for coupling toautothrottle for utilization as a thrust control reference signal.

14. In an autothrottle control system having first and second inputsignals representative of compensated longitudinal acceleration andcompensated air speed error coupled as input signals to an autothrottle;compensating means comprising:

first means including circuit means representative of engine transferfunction for providing a third signal representative of change inthrust;

second means for providing a fourth signal representative of pitchattitude compensated longitudinal acceleration;

third means for providing a fifth signal representative of air speederror;

fourth means comprising summing amplifier means responsive to said thirdand fourth signals for providing a sixth signal;

fifth means comprising washout circuit means responsive to said sixthsignal for providing a first compensation signal;

sixth means comprising summing amplifier means for combining said firstcompensation signal with said fourth signal to provide said first inputsignal to the autothrottle;

seventh means including pseudo integrator circuit means responsive tosaid first compensation signal for providing a second compensationsignal; and

eighth means comprising summing amplifier circuit means for combiningsaid second compensation signal with said fifth signal for providingsaid second input signal to the autothrottle.

15. A system for computing speed perturbations due to path deviations ofan aircraft to provide first and second compensating signals forcoupling respectively to autothrottle control system input signalcontrol channels representative of longitudinal acceleration and airspeed error comprising:

first means for generating a signal representative of acceleration ofsaid aircraft due to change in flight path angle;

a washout circuit responsive to said singal representative ofacceleration of said aircraft due to change where g is gravityacceleration constant, 0 is pitch attitude, C is drag coefficient changeper unit change in a q is dynamic pressure, s is wing area,

w is weight, and a is angle of attack.

* I F I!

1. In combination an autothrottle control system for an aircraft havinga first input coupled to first means for providing a signalrepresentative of longitudinal acceleration information of saidaircraft, and a second input coupled to second means for providing asignal representative of air speed error of said aircraft; signalprocessing means responsive to signals representative of pitch attitudeand angle of attack information of said aircraft for providing a firstcompensation signal representative of longitudinal acceleration of saidaircraft induced by short term flight path aNgle changes and a secondcompensation signal representative of the deviation of air speed due toshort term flight path angle changes; third means for combining saidfirst compensation signal with said signal representative oflongitudinal acceleration information of said aircraft; and fourth meansfor combining said second compensation signal with said signalrepresentative of air speed error of said aircraft.
 2. The inventionaccording to claim 1 wherein said third and fourth means comprisesumming amplifiers.
 3. In combination; an aircraft autothrottle havingfirst and second input terminals for receiving signals representative oflongitudinal acceleration and air speed error; pitch attitude sensingmeans for providing a first signal representative of pitch attitude ofthe aircraft; angle of attack sensing means for providing a secondsignal representative of angle of attack of the aircraft; first summingamplifier means for combining said first and second signals andproviding a third signal; first washout circuit means responsive to saidthird signal for providing a first compensation signal; attitudecompensated longitudinal accelerometer means for providing a fourthsignal representative of longitudinal acceleration; second summingamplifier means responsive to said fourth signal and said firstcompensation signal for providing a signal representative of compensatedlongitudinal acceleration; first coupling means for coupling said signalrepresentative of compensated longitudinal acceleration to said firstinput terminal; air speed error sensing means coupled to demodulatorcircuit means for providing a signal representative of air speed errorof the aircraft; pseudo integrator circiut means responsive to saidfirst compensation signal for providing a second compensation signal;third summing amplifier means responsive to said second compensationsignal and said signal representative of air speed error for providing asignal representative of compensated air speed error; and, secondcoupling means for coupling said signal representative of compensatedair speed error to said second input terminal.
 4. In an autothrottlecontrol system, an improvement for inhibiting autothrottle response tospeed perturbations induced by flight path deviations comprising: firstmeans for generating a first compensation signal in accordance with theexpression
 5. In an aircraft authrottle control system having a firstautothrottle input signal representative of longitudinal accelerationand a second input signal representative of air speed error: first meansfor generating a third signal representative of change in flight pathangle; second means for generating a fourth signal representative ofchange in drag with respect to change in angle of attack multiplied bythe product of dynamic pressure times wing area divided by the weight ofthe aircraft; third means for summing said thirD and fourth signalsthereby providing a fifth signal; a washout circuit; fourth means formultiplying said fifth signal by the gravity acceleration constant andcoupling the product to said washout circuit to provide a firstcompensation signal; fifth means responsive to said first compensationsignal for providing pseudo integration of said first compensationsignal to provide a second compensation signal; sixth means for summingsaid first compensation signal with said first autothrottle input signalto provide a compensated first autothrottle input signal; and seventhmeans for summing said second compensation signal with said secondautothrottle input signal to provide a compensated second autothrottleinput signal.
 6. In an autothrottle for an aircraft having first andsecond autothrottle input signals representative of longitudinalacceleration and air speed error, means for compensating said first andsecond autothrottle input signals comprising: first summing circuitmeans having a plurality of input terminals and an output terminal;throttle servo-tachometer means, circuit means representative of enginetransfer function of the aircraft, and pseudo integrator circuit meansconnected in series circuit with a first of said plurality of inputterminals; second circuit means for coupling said first signalrepresentative of longitudinal acceleration to a second of saidplurality of input terminals; washout circuit means coupled to saidoutput terminal for providing a first compensating signal; third circuitmeans for combining said first autothrottle input signal representativeof longitudinal acceleration with said first compensating signal toprovide a compensated first autothrottle input signal; further pseudointegrator circuit means responsive to said first compensating signalfor providing a second compensating signal; and fourth circuit means forcombining said second input signal representative of air speed errorwith said second compensating signal to provide a compensated secondautothrottle input signal.
 7. The invention of claim 6 wherein the timeconstant of said washout circuit means and the further time constant ofsaid further pseudo integrator circuit means vary as a function of thesum of air speed and forward acceleration of said aircraft.
 8. Theinvention of claim 6 wherein said washout circuit means and said furtherpseudo integrator circuit means comprise respectively first and secondvariable time constant filtering means.
 9. The invention according toclaim 8 further including time constant programming means responsive toincreasing air speed errors and forward accelerations of said aircraftfor decreasing the respective time constants of said first and secondvariable time constant filtering means.
 10. The invention according toclaim 8 further including time constant programming means formultiplying the respective loop gains of said first and second variabletime constant filtering means.
 11. The invention according to claim 10wherein said time constant programming means comprises: first amplifiermeans responsive to air speed error for providing an amplified air speederror signal; second amplifier means responsive to forward accelerationfor providing an amplified forward acceleration signal; a positive biassignal source; and means for providing the absolute sum of saidamplified error signal and said forward acceleration signal and addingto said sum said positive bias signal to provide a programming controlsignal for multiplying said respective loop gains of said first andsecond variable time constant filtering means.
 12. The inventionaccording to claim 11 wherein the gain factor of said first amplifiermeans is 0.4 per knot air speed error and the gain factor of said secondamplifier means is 5 per knot per second acceleration.
 13. In anaircraft autothrottle control system: first circuit means for providinga firSt signal representative of rate of change in throttle position;second circuit means representative of engine transfer function of saidaircraft responsive to said first signal for providing a second signalrepresentative of rate of change of thrust; pseudo integrator circuitmeans responsive to said second signal for providing a third signalrepresentative of short term acceleration of said aircraft due tothrust; third circuit means for providing a fourth signal representativeof longitudinal acceleration of said aircraft; fourth circuit meanscomprising a summing amplifier circuit responsive to said third andfourth signals for providing a fifth signal representative ofacceleration of said aircraft due to deviation from the flight path;fifth circuit means comprising a washout circuit responsive to saidfifth signal for providing a compensation signal; sixth circuit meanscomprising a summing amplifier responsive to said fifth signal and saidcompensation signal for providing a signal representative of compensatedlongitudinal acceleration for coupling to autothrottle for utilizationas a thrust control damping signal; seventh circuit means comprising apseudo integrator circuit responsive to said compensation signal forproviding a further compensation signal representative of air speederror due to deviation from flight path; eighth circuit means forproviding a sixth signal representative of air speed error; and ninthcircuit means comprising a summing amplifier responsive to said sixthsignal and said further compensation signal for providing a signalrepresentative of compensated air speed error for coupling toautothrottle for utilization as a thrust control reference signal. 14.In an autothrottle control system having first and second input signalsrepresentative of compensated longitudinal acceleration and compensatedair speed error coupled as input signals to an autothrottle;compensating means comprising: first means including circuit meansrepresentative of engine transfer function for providing a third signalrepresentative of change in thrust; second means for providing a fourthsignal representative of pitch attitude compensated longitudinalacceleration; third means for providing a fifth signal representative ofair speed error; fourth means comprising summing amplifier meansresponsive to said third and fourth signals for providing a sixthsignal; fifth means comprising washout circuit means responsive to saidsixth signal for providing a first compensation signal; sixth meanscomprising summing amplifier means for combining said first compensationsignal with said fourth signal to provide said first input signal to theautothrottle; seventh means including pseudo integrator circuit meansresponsive to said first compensation signal for providing a secondcompensation signal; and eighth means comprising summing amplifiercircuit means for combining said second compensation signal with saidfifth signal for providing said second input signal to the autothrottle.15. A system for computing speed perturbations due to path deviations ofan aircraft to provide first and second compensating signals forcoupling respectively to autothrottle control system input signalcontrol channels representative of longitudinal acceleration and airspeed error comprising: first means for generating a signalrepresentative of acceleration of said aircraft due to change in flightpath angle; a washout circuit responsive to said singal representativeof acceleration of said aircraft due to change in flight path angle forproviding said first compensating signal; low pass filter circuit meansresponsive to said first compensating signal for providing said secondcompensating signal; and wherein said first means comprises means forgenerating a signal representative of